The formin protein FHOD1 is expressed in a variety of tissues and has been implicated in cell migration. Our goals are to determine the role of FHOD1 in the regulation of cellular responses to the extracellular matrix and to elucidate the mechanisms by which FHOD1 influences cytoskeletal architecture and signal transduction events. The central hypothesis of this application is that FHOD1 modulates cell migration via regulation of Rho, Rac and Ras GTPase-mediated events. We have recently demonstrated co-precipitation of FHOD1 with the MAP kinase pathway components, Raf-1, kinase suppressor of Ras (KSR) and ERK. These findings represent the first example of a formin protein physically interacting with any MAP kinase component and represent a new and exciting aspect of formin protein biology. In addition, we have demonstrated an interaction between FHOD1 and actin, and we have shown that a C-terminal mutant of FHOD1 stimulates ERK-dependent serum response element driven gene expression and induces the formation of thick actin stress fibers in a Rho-dependent manner. We present two specific aims to test our hypothesis: 1) Further investigate the relationship between FHOD1 and the KSR/ERK/MAP kinase pathway. Our working hypothesis is that FHOD1's effects on cell migration are dependent on interactions with the ERK MAP kinase/KSR scaffold or on ERK activation; and 2) Determine if the biological effects of FHOD1 are dependent on Rho or Rac. The proposed work is innovative because it capitalizes on the novel findings that FHOD1 modulates cell migration and that FHOD1 interacts with multiple members of the ERK pathway. We expect to identify mechanisms by which FHOD1 regulates the cytoskeleton and signal transduction and determine its contribution to cell migration. These results will be significant because they will enhance our understanding of celI-ECM interactions and may lead to development of pharmacologic interventions aimed at maintaining or re-establishing optimal tissue integrity.